This is just the next step in killing third-party apps. Twitter doesn’t have the guts to just end them outright, so they’re just gradually inflicting passive-aggressive wounds over time to quietly shove them into the sunset.
We’re all just one compelling feature away from leaving our third-party apps on our own. For some of us, this full-archive search will be that feature. What’s next remains to be seen — I suspect direct-message enhancements may be — but I bet third-party clients will lose half of their users within two years without Twitter ever having to explicitly kill them.
More and more people I know and talk to on Twitter use the first-party, official client --- and for good reason(s). I've long been a diehard Tweetbot user, but Marco's sentiments are right on: Twitter wants apps like Tweetbot (and Twitterrific) to die.
I love Tweetbot, but maybe it's time to see what the future (read: Twitter for iOS) inevitably looks like.